Sarcoplasmic reticulum Ca2+ transport and gene expression in congestive heart failure are modified by imidapril treatment

Mechanisms for the development of heart failure and improvement of cardiac function by angiotensin-converting enzyme inhibitors

Angiotensin-converting enzyme (ACE) inhibitors, which prevent the conversion of angiotensin I to angiotensin II, are well-known for the treatments of cardiovascular diseases, such as heart failure, hypertension and acute coronary syndrome. Several of these inhibitors including captopril, enalapril, ramipril, zofenopril and imidapril attenuate vasoconstriction, cardiac hypertrophy and adverse cardiac remodeling, improve clinical outcomes in patients with cardiac dysfunction and decrease mortality. Extensive experimental and clinical research over the past 35 years has revealed that the beneficial effects of ACE inhibitors in heart failure are associated with full or partial prevention of adverse cardiac remodeling. Since cardiac function is mainly determined by coordinated activities of different subcellular organelles, including sarcolemma, sarcoplasmic reticulum, mitochondria and myofibrils, for regulating the intracellular concentration of Ca2+ and myocardial metabolism, there is ample evidence to suggest that adverse cardiac remodelling and cardiac dysfunction in the failing heart are the consequence of subcellular defects. In fact, the improvement of cardiac function by different ACE inhibitors has been demonstrated to be related to the attenuation of abnormalities in subcellular organelles for Ca2+-handling, metabolic alterations, signal transduction defects and gene expression changes in failing cardiomyocytes. Various ACE inhibitors have also been shown to delay the progression of heart failure by reducing the formation of angiotensin II, the development of oxidative stress, the level of inflammatory cytokines and the occurrence of subcellular defects. These observations support the view that ACE inhibitors improve cardiac function in the failing heart by multiple mechanisms including the reduction of oxidative stress, myocardial inflammation and Ca2+-handling abnormalities in cardiomyocytes.

Role of angiotensin II in the development of subcellular remodeling in heart failure

The development of heart failure under various pathological conditions such as myocardial infarction (MI), hypertension and diabetes are accompanied by adverse cardiac remodeling and cardiac dysfunction. Since heart function is mainly determined by coordinated activities of different subcellular organelles including sarcolemma, sarcoplasmic reticulum, mitochondria and myofibrils for regulating the intracellular concentration of Ca2+, it has been suggested that the occurrence of heart failure is a consequence of subcellular remodeling, metabolic alterations and Ca2+-handling abnormalities in cardiomyocytes. Because of the elevated plasma levels of angiotensin II (ANG II) due to activation of the renin-angiotensin system (RAS) in heart failure, we have evaluated the effectiveness of treatments with angiotensin converting enzyme (ACE) inhibitors and ANG II type 1 receptor (AT1R) antagonists in different experimental models of heart failure. Attenuation of marked alterations in subcellular activities, protein content and gene expression were associated with improvement in cardiac function in MI-induced heart failure by treatment with enalapril (an ACE inhibitor) or losartan (an AT1R antagonist). Similar beneficial effects of ANG II blockade on subcellular remodeling and cardiac performance were also observed in failing hearts due to pressure overload, volume overload or chronic diabetes. Treatments with enalapril and losartan were seen to reduce the degree of RAS activation as well as the level of oxidative stress in failing hearts. These observations provide evidence which further substantiate to support the view that activation of RAS and high level of plasma ANG II play a critical role in inducing subcellular defects and cardiac dys-function during the progression of heart failure.

Oxidative Stress as A Mechanism for Functional Alterations in Cardiac Hypertrophy and Heart Failure

Although heart failure due to a wide variety of pathological stimuli including myocardial infarction, pressure overload and volume overload is associated with cardiac hypertrophy, the exact reasons for the transition of cardiac hypertrophy to heart failure are not well defined. Since circulating levels of several vasoactive hormones including catecholamines, angiotensin II, and endothelins are elevated under pathological conditions, it has been suggested that these vasoactive hormones may be involved in the development of both cardiac hypertrophy and heart failure. At initial stages of pathological stimuli, these hormones induce an increase in ventricular wall tension by acting through their respective receptor-mediated signal transduction systems and result in the development of cardiac hypertrophy. Some oxyradicals formed at initial stages are also involved in the redox-dependent activation of the hypertrophic process but these are rapidly removed by increased content of antioxidants in hypertrophied heart. In fact, cardiac hypertrophy is considered to be an adaptive process as it exhibits either normal or augmented cardiac function for maintaining cardiovascular homeostasis. However, exposure of a hypertrophied heart to elevated levels of circulating hormones due to pathological stimuli over a prolonged period results in cardiac dysfunction and development of heart failure involving a complex set of mechanisms. It has been demonstrated that different cardiovascular abnormalities such as functional hypoxia, metabolic derangements, uncoupling of mitochondrial electron transport, and inflammation produce oxidative stress in the hypertrophied failing hearts. In addition, oxidation of catecholamines by monoamine oxidase as well as NADPH oxidase activation by angiotensin II and endothelin promote the generation of oxidative stress during the prolonged period by these pathological stimuli. It is noteworthy that oxidative stress is known to activate metallomatrix proteases and degrade the extracellular matrix proteins for the induction of cardiac remodeling and heart dysfunction. Furthermore, oxidative stress has been shown to induce subcellular remodeling and Ca²⁺-handling abnormalities as well as loss of cardiomyocytes due to the development of apoptosis, necrosis, and fibrosis. These observations support the view that a low amount of oxyradical formation for a brief period may activate redox-sensitive mechanisms, which are associated with the development of cardiac hypertrophy. On the other hand, high levels of oxyradicals over a prolonged period may induce oxidative stress and cause Ca²⁺-handling defects as well as protease activation and thus play a critical role in the development of adverse cardiac remodeling and cardiac dysfunction as well as progression of heart failure.

Deficiency of MicroRNA miR-1954 Promotes Cardiac Remodeling and Fibrosis

Background Cardiac fibrosis occurs because of disruption of the extracellular matrix network leading to myocardial dysfunction. Angiotensin II (AngII) has been implicated in the development of cardiac fibrosis. Recently, microRNAs have been identified as an attractive target for therapeutic intervention in cardiac pathologies; however, the underlying mechanism of microRNAs in cardiac fibrosis remains unclear. Next-generation sequencing analysis identified a novel characterized microRNA, miR-1954, that was significantly reduced in AngII-infused mice. The finding led us to hypothesize that deficiency of miR-1954 triggers cardiac fibrosis. Methods and Results A transgenic mouse was created using α-MHC (α-myosin heavy chain) promoter and was challenged with AngII infusion. AngII induced cardiac hypertrophy and remodeling. The in vivo overexpression of miR-1954 showed significant reduction in cardiac mass and blood pressure in AngII-infused mice. Further analysis showed significant reduction in cardiac fibrotic genes, hypertrophy marker genes, and an inflammatory gene and restoration of a calcium-regulated gene (Atp2a2 [ATPase sarcoplasmic/endoplasmic reticulum Ca2+ transporting 2]; also known as SERCA2), but no changes were observed in apoptotic genes. THBS1 (thrombospondin 1) is indicated as a target gene for miR-1954. Conclusions Our findings provide evidence, for the first time, that miR-1954 plays a critical role in cardiac fibrosis by targeting THBS1. We conclude that promoting the level of miR-1954 would be a promising strategy for the treatment of cardiac fibrosis.

The pathophysiology of myocardial infarction-induced heart failure

Heart failure (HF) is a multifactorial disorder and is usually the end stage of many cardiovascular diseases (CVD). HF presents one of the highest morbidity and mortality indices worldwide and high costs to public health organizations. Myocardial infarction (MI) is the most prevalent CVD in the Western world and leads to HF when its management is inadequate. It has a destructive potential for heart cells and abruptly reduces the cardiac output, a clinical condition known as heart dysfunction that might progress to HF. Many acute and chronic adaptations occur due to MI that progress to HF, e.g., neurohumoral hyperactivity, inflammatory response and cardiac remodeling. Herein, we reviewed in simplistic manner the processes involved in setting of MI until the establishment of HF.

Carbon dioxide water-bath treatment augments peripheral blood flow through the development of angiogenesis

In this study, we investigated the effects of CO₂ water-bath therapy on blood flow and angiogenesis in the ischemic hind limb, as well as some plasma angiogenic factors in peripheral ischemic model. The hind limb ischemia was induced by occluding the femoral artery for 2 weeks in rats and treated with or without CO₂ water-bath therapy at 37 °C for 4 weeks (20 min treatment every day for 5 days per week). The peak blood flow and minimal and mean blood flow in the ischemic skeletal muscle were markedly increased by the CO₂ water-bath therapy. This increase in blood flow was associated with development of angiogenesis in the muscle, as well as reduction in the ischemia-induced increase in plasma malondialdehyde levels. Although plasma vascular endothelial growth factor and nitric oxide levels were increased in animals with peripheral ischemia, the changes in these biomarkers were not affected by CO₂ water-bath therapy. These results suggest that augmentation of blood flow in the ischemic hind limb by CO₂ water-bath therapy may be due to the development of angiogenesis and reduction in oxidative stress.

Suppression of phosphorylated MAPK and caspase 3 by carbon dioxide

Although CO₂ is produced during the oxidation of different substrates in all types of cells, the role of this gas in the regulation of cellular function is not clearly understood. Since changes in several signal transduction as well as apoptotic, anti-apoptotic, and other proteins are known to modify cellular function, we investigated if some of these proteins are altered upon incubating the rat hind leg skeletal muscle in a medium enriched with CO₂ (1000-1200 ppm) for 30 min. CO₂ was observed to depress phosphorylated levels of ERK1 (P44) and ERK2 (P42) without affecting the unphosphorylated content of these MAPK proteins. On the other hand, no change in p38 MAPK protein was found but the content of its degradation product 30 kDa proteins (both phosphorylated and unphosphorylated) was decreased. No alterations in the content of other signaling proteins (PKA and Akt), inflammatory molecule (TNF-α), and vascular endothelial growth factor (VEGF) were seen upon exposure of the muscle to CO₂. The content for apoptotic and anti-apoptotic proteins (Bad and Bcl2), except for a decrease in caspase 3, were also not affected by CO₂. These results indicate that CO₂ may serve as a gasotransmitter to regulate cellular function by depressing MAPK and caspase 3 activities.

Involvement of the dual-specificity tyrosine phosphorylation-regulated kinase 1A-alternative splicing factor-calcium/calmodulin-dependent protein kinase IIδ signaling pathway in myocardial infarction-induced heart failure of rats

BACKGROUND

Alternative splicing factor (ASF)-regulated alternative splicing of calcium/calmodulin-dependent protein kinase IIδ (CaMKIIδ) plays an important role in pathologic cardiac remodeling. ASF can be phosphorylated by dual-specificity tyrosine phosphorylation-regulated kinase 1A (Dyrk1A). This study aimed to investigate the possible involvement of the Dyrk1A-ASF-CaMKIIδ signaling pathway in the progression of myocardial infarction (MI)-induced heart failure (HF).

METHODS AND RESULTS

MI in rats was induced by means of left anterior descending coronary artery ligation. Seven weeks after MI, the increase in left ventricular internal diameter at end-diastole (LVIDd), and the decrease in both ejection fraction (EF) and fractional shortening (FS) indicated that MI rats had developed HF. Quantitative real time reverse-transcription polymerase chain reaction indicated the dysregulation of CaMKIIδ alternative splicing, ie, up-regulation of CaMKIIδA and CaMKIIδC and down-regulation of CaMKIIδB in the hearts of HF rats. Electrophoresis and immunostaining revealed that HF activated the phosphorylation of ASF and affected its subcellular localization. Western blot analysis demonstrated a significant elevation in the activity and expression of Dyrk1A in HF rats. Inversely, treatment of MI-induced HF rats with Dyrk1A inhibitor, either harmine or EGCG, improved the symptoms of HF, reversed the molecular changes of Dyrk1A and ASF, and regulated alternative splicing of CaMKIIδ in HF rats.

CONCLUSIONS

Enhanced activation of Dyrk1A-ASF-CaMKIIδ signaling pathway may underlie the mechanisms of HF after MI, and Dyrk1A inhibition may contribute to inactivation of this pathway and thereby retard the progression of MI-induced HF.

Atrial Natriuretic Peptide Locally Counteracts the Deleterious Effects of Cardiomyocyte Mineralocorticoid Receptor Activation

Background—

The endocrine balance between atrial natriuretic peptide (ANP) and the renin–angiotensin–aldosterone system is critical for the maintenance of arterial blood pressure and volume homeostasis. This study investigated whether a cardiac imbalance between ANP and aldosterone, toward increased mineralocorticoid receptor (MR) signaling, contributes to adverse left ventricular remodeling in response to pressure overload.

Methods and Results—

We used the MR-selective antagonist eplerenone to test the role of MRs in mediating pressure overload–induced dilatative cardiomyopathy of mice with abolished local, cardiac ANP activity. In response to 21 days of transverse aortic constriction, mice with cardiomyocyte-restricted inactivation (knockout) of the ANP receptor (guanylyl cyclase [GC]-A) or the downstream cGMP-dependent protein kinase I developed enhanced left ventricular hypertrophy and fibrosis together with contractile dysfunction. Treatment with eplerenone (100 mg/kg/d) attenuated left ventricular hypertrophy and fully prevented fibrosis, dilatation, and failure. Transverse aortic constriction induced the cardiac expression of profibrotic connective tissue growth factor and attenuated the expression of SERCA2a (sarcoplasmic reticulum Ca 2+ -ATPase) in knockout mice, but not in controls. These genotype-dependent molecular changes were similarly prevented by eplerenone. ANP attenuated the aldosterone-induced nuclear translocation of MRs via GC-A/cGMP-dependent protein kinase I in transfected HEK 293 (human embryonic kidney) cells. Coimmunoprecipitation and fluorescence resonance energy transfer experiments demonstrated that a population of MRs were membrane associated in close interaction with GC-A and cGMP-dependent protein kinase I and, moreover, that aldosterone caused a conformational change of this membrane MR/GC-A protein complex which was prevented by ANP.

Conclusions—

ANP counter-regulates cardiac MR activation in hypertensive heart disease. An imbalance in cardiac ANP/GC-A (inhibition) and aldosterone/MR signaling (augmentation) favors adverse cardiac remodeling in chronic pressure overload.

Expression of Ca(2+)-ATPase in sarcoplasmic reticulum in rat cardiomyocytes during experimental postinfarction cardiosclerosis and diabetes mellitus

We studied the expression of Ca(2+)-ATPase in sarcoplasmic reticulum of rat cardiomyocytes during isolated and combined development of postinfarction cardiosclerosis and diabetes mellitus. Postinfarction cardiosclerosis was formed within 6 weeks after coronary artery occlusion. Diabetes mellitus developed within 6 weeks after intraperitoneal injection of streptozotocin (60 mg/kg). Ca(2+)-ATPase in homogenate of rat myocardium was assayed by immunoblotting. Ischemic and diabetic remodeling of the myocardium was associated with reduced expression of Ca(2+)-ATPase in the sarcoplasmic reticulum. Combined pathology was characterized by minimum decrease in the level of this protein. It was concluded that induction of diabetes mellitus at the early stage of postinfarction cardiosclerosis triggered adaptive mechanisms that prevent the decrease in Ca(2+)-ATPase level in the sarcoplasmic reticulum of cardiomyocytes.

Reversal of subcellular remodelling by losartan in heart failure due to myocardial infarction

This study tested the reversal of subcellular remodelling in heart failure due to myocardial infarction (MI) upon treatment with losartan, an angiotensin II receptor antagonist. Twelve weeks after inducing MI, rats were treated with or without losartan (20 mg/kg; daily) for 8 weeks and assessed for cardiac function, cardiac remodelling, subcellular alterations and plasma catecholamines. Cardiac hypertrophy and lung congestion in 20 weeks MI-induced heart failure were associated with increases in plasma catecholamine levels. Haemodynamic examination revealed depressed cardiac function, whereas echocardiographic analysis showed impaired cardiac performance and marked increases in left ventricle wall thickness and chamber dilatation at 20 weeks of inducing MI. These changes in cardiac function, cardiac remodelling and plasma dopamine levels in heart failure were partially or fully reversed by losartan. Sarcoplasmic reticular (SR) Ca²⁺-pump activity and protein expression, protein and gene expression for phospholamban, as well as myofibrillar (MF) Ca²⁺-stimulated ATPase activity and α-myosin heavy chain mRNA levels were depressed, whereas β-myosin heavy chain expression was increased in failing hearts; these alterations were partially reversed by losartan. Although SR Ca²⁺-release activity and mRNA levels for SR Ca²⁺-pump were decreased in failing heart, these changes were not reversed upon losartan treatment; no changes in mRNA levels for SR Ca²⁺-release channels were observed in untreated or treated heart failure. These results suggest that the partial improvement of cardiac performance in heart failure due to MI by losartan treatment is associated with partial reversal of cardiac remodelling as well as partial recovery of SR and MF functions.

Fosinopril attenuates the doxorubicin-induced cardiomyopathy by restoring the function of sarcoplasmic reticulum

Fosinopril, an angiotensin-converting enzyme inhibitor, is known to attenuate cardiomyopathy induced by doxorubicin (DOX); however, the mechanisms of this cardioprotection are not fully elucidated yet. In the present study, experimental cardiomyopathy was induced in rats by administration of DOX with or without co-treatment with fosinopril. Fosinopril was utilized on day 1 or 14 of the treatment with DOX to compare efficacies of early versus late co-treatments. We observed that fosinopril attenuated changes induced by DOX (e.g., less increased heart and left ventricular weights, diminished lung congestion and ascites, attenuated LVEDP and LVSP, and less decreased +dP/dt and -dP/dt). Further, fosinopril diminished the levels of markers of cardiac toxicity (i.e., plasma levels and activities of cardiac enzymes and proteins AST, LDH, CPK, cTnI, and BNP). Fosinopril also prevented DOX-induced decreases in Ca(2+) uptake and restored activity of Ca(2+)-stimulated ATPase in left ventricular sarcoplasmic reticulum. We next tested whether the improved Ca(2+) transport activity in sarcoplasmic reticulum was due to modulation of SERCA2 and phospholamban expressions by fosinopril. Fosinopril attenuated the decrease in SERCA2 and phospholamban expressions caused by DOX. In conclusion, cardioprotective effects of fosinopril in the DOX-induced cardiomyopathy appear to be due to its ability to prevent remodeling of the cardiac sarcoplasmic reticulum membrane.

Cardiac remodeling and subcellular defects in heart failure due to myocardial infarction and aging

Although several risk factors including hypertension, cardiac hypertrophy, coronary artery disease, and diabetes are known to result in heart failure, elderly subjects are more susceptible to myocardial infarction and more likely to develop heart failure. This article is intended to discuss that cardiac dysfunction in hearts failing due to myocardial infarction and aging is associated with cardiac remodeling and defects in the subcellular organelles such as sarcolemma (SL), sarcoplasmic reticulum (SR), and myofibrils. Despite some differences in the pattern of heart failure due to myocardial infarction and aging with respect to their etiology and sequence of events, evidence has been presented to show that subcellular remodeling plays a critical role in the occurrence of intracellular Ca(2+)-overload and development of cardiac dysfunction in both types of failing heart. In particular, alterations in gene expression for SL and SR proteins induce Ca(2+)-handling abnormalities in cardiomyocytes, whereas those for myofibrillar proteins impair the interaction of Ca(2+) with myofibrils in hearts failing due to myocardial infarction and aging. In addition, different phosphorylation mechanisms, which regulate the activities of Ca(2+)-cycling proteins in SL and SR membranes as well as Ca(2+)-binding proteins in myofibrils, become defective in the failing heart. Accordingly, it is suggested that subcellular remodeling involving defects in Ca(2+)-handling and Ca(2+)-binding proteins as well as their regulatory mechanisms is intimately associated with cardiac remodeling and heart failure due to myocardial infarction and aging.

Involvement of sarcoplasmic reticulum in changing intracellular calcium due to Na+/K+-ATPase inhibition in cardiomyocytes

Earlier studies have demonstrated that ouabain-induced increase in [Ca2+]i, as a consequence of sarcolemma (SL) Na+/K+-ATPase inhibition, is associated with activation of both the SL Na+/Ca2+ exchanger and SL Ca2+ channels. In view of the importance of sarcoplasmic reticulum (SR) in the regulation of [Ca2+]i, this study examined the role of SR in ouabain-induced increase in [Ca2+]i in both quiescent and KCl-depolarized cardiomyocytes. For this purpose, adult rat cardiomyocytes were loaded with fura-2 and ouabain-induced changes in [Ca2+]i were monitored upon treatment with or without different agents that are known to influence Ca2+ handling by the intracellular organelles. Ouabain not only increased the basal [Ca2+]i and augmented KCl-induced increase in [Ca2+]i but also produced similar effects on the ATP-induced increase in [Ca2+]i. Treatments of cardiomyocytes with caffeine, ryanodine, or cyclopiazonic acid, which affect SR Ca2+ stores, attenuated the ouabain-induced increase in basal Ca2+ as well as augmentation of the KCl response. Both ryanodine and cyclopiazonic acid produced additional effects, when used in combination with a SL Ca2+ channel inhibitor (verapamil), but not with a Na+/Ca2+ exchange inhibitor (KB-R7943). Inhibitors of Ca2+/calmodulin kinase, protein kinase A, and inositol-3-phosphate receptors were also observed to depress the ouabain-induced increase in [Ca2+]i in cardiomyocytes. On the other hand, mitochondrial Ca2+ transport inhibitors did not exert any effect on the ouabain-induced alterations in [Ca2+]i in cardiomyocytes. Furthermore, ouabain did not show any direct effect on the Ca2+ uptake and Ca2+ release activities of SR or mitochondria. These results suggest an indirect involvement of SR Ca2+ stores in the ouabain-induced increase in [Ca2+]i in cardiomyocytes and indicate the participation of both Ca2+-induced Ca2+ release and regulatory mechanisms in this action.

Losartan reduces mortality in a genetic model of heart failure

Altered Ca(2+) homoeostasis accompanies heart failure. As a model of heart failure, transgenic mice (TG) with selective overexpression of calsequestrin (CSQ) in the heart were used. CSQ is the main Ca(2+) binding protein in the lumen of the junctional sarcoplasmic reticulum. Overexpression of CSQ leads to hypertrophy, fibrosis, heart failure, cardiac arrhythmias, and ultimately premature death compared to littermate controls (WT). In the present study, cardiac hypertrophy was noted at 2 months of age (relative heart weight 6.4 +/- 0.2 mg/g in WT and 11.2 +/- 0.3 mg/g in TG, n = 7, p < 0.05) which progressed at 5 months of age (relative heart weight 15.5 +/- 1.1 mg/g in TG, n = 11). Furthermore, an increased degree of fibrosis (from 0.29 +/- 0.04 in WT to 0.77 +/- 0.06 in TG, n = 8, p < 0.05) was quantified by sirius red staining. Cardiac function was greatly impaired in TG as exemplified by reduced pressure development and cardiac arrhythmias. It is hypothesized that losartan, an inhibitor of angiotensin II receptors, might be able to attenuate these detrimental effects. Hence, TG and WT were treated for 1 or 4 months perorally with losartan (5 mg/kg/day) or solvent alone (control conditions) starting at 4 weeks of age. Under control conditions, none of the WT died within the observation period whereas all TG died within 9 months. Losartan treatment reduced the mortality of TG: Mean life span was raised from 116 to 193 days (n = 18 end, p < 0.05). Likewise, losartan reduced relative heart weight and the degree of fibrosis. In addition, losartan improved hemodynamic parameters, like left ventricular pressure and its first derivative. However, losartan treatment did not modify overexpression of CSQ in the heart of TG. These results imply that the angiotensin II receptor (type 1) contributes to heart failure due to CSQ overexpression, as its blockade improved survival.

Both enalapril and losartan attenuate sarcolemmal Na+-K+-ATPase remodeling in failing rat heart due to myocardial infarctionThis article is one of a selection of papers published in the special issue Bridging the Gap: Where Progress in Cardiovascular and Neurophysiologic Research Meet

To investigate the mechanisms underlying the depressed sarcolemmal (SL) Na+-K+-ATPase activity in congestive heart failure (CHF), different isoforms and gene expression of Na+-K+-ATPase were examined in the failing left ventricle (LV) at 8 weeks after myocardial infarction (MI). In view of the increased activity of renin–angiotensin system (RAS) in CHF, these parameters were also studied after 5 weeks of treatment with enalapril (10 mg·kg–1·day–1), an angiotensin-converting enzyme inhibitor, and losartan (20 mg·kg–1·day–1), an angiotensin II type 1 receptor antagonist, starting at 3 weeks after the coronary ligation in rats. The infarcted animals showed LV dysfunction and depressed SL Na+-K+-ATPase activity. Protein content and mRNA levels for Na+-K+-ATPase α2isoform were decreased whereas those for Na+-K+-ATPase α3isoform were increased in the failing LV. On the other hand, no significant changes were observed in protein content or mRNA levels for Na+-K+-ATPase α1and β1isoforms. The treatment of infarcted animals with enalapril or losartan improved LV function and attenuated the depression in Na+-K+-ATPase α2isoform as well as the increase in α3isoform, at both the protein and mRNA levels; however, combination therapy with enalapril and losartan did not produce any additive effects. These results provide further evidence that CHF due to MI is associated with remodeling of SL membrane and suggest that the blockade of RAS plays an important role in preventing these alterations in the failing heart.

Antiplatelet therapy mitigates cardiac remodeling and dysfunction in congestive heart failure due to myocardial infarctionThis article is one of a selection of papers published in the special issue Bridging the Gap: Where Progress in Cardiovascular and Neurophysiologic Research Meet

Antiplatelet agents such as sarpogrelate (SAR), a 5-hydroxytryptamine antagonist, and cilostazol (CIL), a phosphodiesterase-III inhibitor, are used in the management of peripheral vascular disease. In this study, we tested the hypothesis that both SAR and CIL prevent cardiac remodeling and improve cardiac function in congestive heart failure (CHF) due to myocardial infarction (MI). Post-MI rats (3 weeks after the occlusion of coronary artery) received either vehicle (MI+V, n = 36), SAR (MI+SAR; 5 mg·kg–1·day–1, n = 35) or CIL (MI+CIL; 5 mg·kg–1·day–1, n = 34) from day 21 to day 56. Sham-operated rats (n = 29) served as controls. Electrocardiographic, echocardiographic, and hemodynamic parameters were measured on day 56. Treatment of infarcted animals with SAR or CIL significantly improved the left ventricular (LV) dimensions, LV fractional shortening, cardiac output, stroke volume, mean arterial pressure, LV diastolic function, and LV systolic pressure, as well as rates of LV pressure development and pressure decay. Although cardiac hypertrophy was reduced, both SAR and CIL had no effect on infarct size or MI-associated QTc prolongation. However, SAR decreased whereas CIL increased the incidence of ventricular arrhythmias and the mean number of episodes in infarcted animals. Mortality during the treatment period was decreased by 17% with SAR and increased by 10% with CIL, but these changes were not significant statistically. The data in this study suggest that both SAR and CIL prevent cardiac remodeling and improve cardiac function in MI-induced CHF; however, CIL unlike SAR increased the incidence of arrhythmias and adversely affected patient mortality.

Antiplatelet therapy attenuates subcellular remodelling in congestive heart failure

Antiplatelet agents, sarpogrelate (SAR), a 5-HT(2A) receptor antagonist, and cilostazol (CIL), a phosphodiesterase III (PDE-III) inhibitor, are used for the treatment of peripheral vascular disease. We tested whether these agents affect cardiac function and subcellular remodelling in congestive heart failure (CHF) induced by myocardial infarction (MI). Three weeks after MI, rats were treated daily with 5 mg/kg SAR or CIL as well as vehicle for 5 weeks. Sham-operated animals served as controls. At end of the treatment period, haemodynamic measurements were performed and the left ventricle was processed for the determination of sarcoplasmic reticulum (SR) Ca(2+)-uptake and -release activities, and expression of SR Ca(2+)-pump, phospholamban and ryanodine receptors, as well as myofibrillar ATPase activities, expression of alpha- and beta-myosin heavy chain (MHC) isoforms, and phosphorylation of phospholamban and cardiac troponin-I (c Tn-I). Marked haemodynamic changes in the MI-induced CHF were associated with depressions in SR Ca (+)-uptake and -release activities as well as in protein content and gene expression for SR proteins. Furthermore, myofibrillar Ca(2+)-stimulated ATPase activity, as well as protein content and gene expression for alpha-MHC were decreased whereas those for beta-MHC were increased in the failing heart. Also, phosphorylation levels of phospholamban and cTn-I were reduced in failing hearts. The MI-associated changes in cardiac function, SR and myofibillar activities, as well as SR and myofibrillar protein and gene expression were attenuated by treatment with SAR or CIL. The results suggest that SAR and CIL improve cardiac function by ameliorating subcellular remodelling in the failing heart and indicate the potential therapy of CHF with antiplatelet agents.

Time course of changes in the expression of DHPR, RyR(2), and SERCA2 after myocardial infarction in the rat left ventricle

Postinfarction left ventricular remodeling leads to the functional decline of the left ventricle (LV). Since dihydropyridine receptor (DHPR), ryanodine receptor (RyR(2)), and sarco-endoplasmic reticulum (SR) Ca(2+)-ATPase2 (SERCA2a) play a major role in the contractility of the heart, the aim of our study was to evaluate the time course of changes in the expression of these proteins 1 day, 2 weeks and 4 weeks after myocardial infarction (MI). Myocardial infarction was produced by ligation of left anterior descending coronary artery of the rat. Transthoracic echocardiography was performed to characterize structural and functional changes after MI. To evaluate protein mRNA levels and the relative amount of proteins, real-time quantitative RT-PCR and Western blotting were used. LV ejection fraction and fractional shortening decreased significantly during the 4-week follow-up period (P < 0.001). Typical features of LV remodeling after MI were seen, with a decrease in anterior wall thickness (P < 0.001) and dilatation of the LV (P < 0.001). Expression of DHPR and RyR(2) mRNAs decreased and Serca2a mRNA tended to decrease 1 day after MI (P < 0.001, P < 0.01 and P = 0.06, respectively), followed by recovery of the expression during the next 4 weeks. In the infarcted hearts the quantities of SERCA2 proteins in the LV were significantly decreased at the time of 4 weeks. In conclusion, MI was associated with transient decrease in the expression of the DHPR and RyR(2) mRNAs and a reduced quantity of SERCA2 proteins in the LV. Since they have a key role in the contraction of the heart, changes in the expression of these proteins may be important regulators of LV systolic function after MI.

Arrhythmogenic Ion-Channel Remodeling in the Heart: Heart Failure, Myocardial Infarction, and Atrial Fibrillation

Rhythmic and effective cardiac contraction depends on appropriately timed generation and spread of cardiac electrical activity. The basic cellular unit of such activity is the action potential, which is shaped by specialized proteins (channels and transporters) that control the movement of ions across cardiac cell membranes in a highly regulated fashion. Cardiac disease modifies the operation of ion channels and transporters in a way that promotes the occurrence of cardiac rhythm disturbances, a process called “arrhythmogenic remodeling.” Arrhythmogenic remodeling involves alterations in ion channel and transporter expression, regulation and association with important protein partners, and has important pathophysiological implications that contribute in major ways to cardiac morbidity and mortality. We review the changes in ion channel and transporter properties associated with three important clinical and experimental paradigms: congestive heart failure, myocardial infarction, and atrial fibrillation. We pay particular attention to K+, Na+, and Ca2+channels; Ca2+transporters; connexins; and hyperpolarization-activated nonselective cation channels and discuss the mechanisms through which changes in ion handling processes lead to cardiac arrhythmias. We highlight areas of future investigation, as well as important opportunities for improved therapeutic approaches that are being opened by an improved understanding of the mechanisms of arrhythmogenic remodeling.

Blockade of the renin-angiotensin system attenuates sarcolemma and sarcoplasmic reticulum remodeling in chronic diabetes

Although the defects in the sarcolemma (SL) and sarcoplasmic reticulum (SR) membranes are known to be associated with cardiac dysfunction in chronic diabetes, very little information regarding the mechanisms of these membrane abnormalities is available in the literature. For this reason, rats were treated daily for 8 weeks with and without enalapril, an angiotensin-converting enzyme inhibitor, or losartan, an angiotensin receptor antagonist, 3 days after inducing diabetes with an injection of streptozocin. Treatment of diabetic animals with both enalapril and losartan attenuated alterations in cardiac function and the left ventricular redox potential without any changes in the increased plasma glucose or reduced plasma insulin levels. The SL Na+-K+ ATPase, Ca2+ pump, Na+-dependent Ca2+-uptake, Ca2+-channel density, and low-affinity Ca2+-binding activities were depressed whereas Ca2+ ecto-ATPase activity was increased in the diabetic heart. Furthermore, the SR Ca2+-release and Ca2+-pump activities in the diabetic hearts were decreased without any changes in the Mg2+-ATPase activity. These alterations in SL and SR membranes in diabetic animals were partly prevented by treatments with enalapril and losartan. The results suggest that the activation of the renin-angiotensin system plays an important role in diabetes-induced changes in SL and SR membranes as well as cardiac function.

Role of subcellular remodeling in cardiac dysfunction due to congestive heart failure

Although alterations in the size and shape of the heart (cardiac remodeling) are considered in explaining cardiac dysfunction during the development of congestive heart failure (CHF), there are several conditions including initial stages of cardiac hypertrophy, where cardiac remodeling has also been found to be associated with either an increased or no change in heart function. Extensive studies have indicated that cardiac dysfunction is related to defects in one or more subcellular organelles such as myofibrils, sarcoplasmic reticulum and sarcolemma, depending upon the stage of CHF. Such subcellular abnormalities in the failing hearts have been shown to occur at both genetic and protein levels. Blockade of the renin-angiotensin system has been reported to partially attenuate changes in subcellular protein, gene expression, functional activities and cardiac performance in CHF. These observations provide support for the role of subcellular remodeling (alterations in molecular and biochemical composition of subcellular organelles) in cardiac dysfunction in the failing heart. On the basis of existing knowledge, it appears that subcellular remodeling during the process of cardiac remodeling plays a major role in the development of cardiac dysfunction in CHF.

Differential changes in β-adrenoceptor signal transduction in left and right ventricles of infarcted ratsThis paper is one of a selection of papers published in this Special issue, entitled Second Messengers and Phosphoproteins—12th International Conference

Although different experimental and clinical studies have revealed varying degrees of defects in β-adrenoceptors (β-ARs) during the development of heart failure, the mechanisms for differences in β-AR signal transduction between the left (LV) and right ventricle (RV) are not understood. Because biochemical alterations in the myocardium depend on the stage of heart disease, this study was undertaken to assess the status of β-ARs in the LV and RV at different stages of heart failure. Myocardial infarction was induced in rats by occluding the left coronary artery for 8 and 24 weeks. The β-AR signal transduction was monitored by measuring β1-AR density, the isoproterenol-induced positive inotropic effect, the increase in [Ca2+]i in cardiomyocytes, and the activation of adenylyl cyclase. The β-AR signal transduction parameters in the 8- and 24-week failing LV were depressed, whereas the RV showed upregulation at 8 weeks and downregulation at 24 weeks of these mechanisms. These results suggest that β-AR-mediated signal transduction in the LV and RV are differentially regulated and are dependent upon the stage of development of congestive heart failure due to myocardial infarction.

Subcellular remodeling as a viable target for the treatment of congestive heart failure

It is now well known that congestive heart failure (CHF) is invariably associated with cardiac hypertrophy, and changes in the shape and size of cardiomyocytes (cardiac remodeling) are considered to explain cardiac dysfunction in CHF. However, the mechanisms responsible for the transition of cardiac hypertrophy to heart failure are poorly understood. Several lines of evidence both from various experimental models of CHF and from patients with different types of CHF have indicated that the functions of different subcellular organelles such as extracellular matrix, sarcolemma, sarcoplasmic reticulum, myofibrils, mitochondria, and nucleus are defective. Subcellular abnormalities for protein contents, gene expression, and enzyme activities in the failing heart become evident as a consequence of prolonged hormonal imbalance, metabolic derangements, and cation maldistribution. In particular, the occurrence of oxidative stress, development of intracellular Ca2+ overload, activation of proteases and phospholipases, and alterations in cardiac gene expression result in changes in the biochemical composition, molecular structure, and function of different subcellular organelles (subcellular remodeling). Not only does subcellular remodeling appear to be intimately involved in the transition of cardiac hypertrophy to heart failure, the mismatching of the function of different subcellular organelles leads to the development of cardiac dysfunction. Although blockade of the renin-angiotensin system, sympathetic nervous system, and various other hormonal actions have been reported to produce beneficial effects on cardiac remodeling and heart dysfunction in CHF, the actions of various cardiac drugs on subcellular remodeling have not been examined extensively. Some recent studies have indicated that both the angiotensin-converting enzyme inhibitors and angiotensin receptor antagonists attenuate changes in sarcolemma, sarcoplasmic reticulum, and myofibril enzyme activities, protein contents, and gene expression, and partly improve cardiac function in the failing hearts. It is suggested that subcellular remodeling is an excellent target for the development of improved drug therapy for CHF. Furthermore, extensive studies should investigate the effects of different agents individually or in combination on reverse subcellular remodeling, cardiac remodeling, and cardiac dysfunction in various experimental models of CHF.

Modification of sarcolemmal Na+-K+-ATPase and Na+/Ca2+exchanger expression in heart failure by blockade of renin-angiotensin system

The activities of both sarcolemmal (SL) Na+-K+-ATPase and Na+/Ca2+exchanger, which maintain the intracellular cation homeostasis, have been shown to be depressed in heart failure due to myocardial infarction (MI). Because the renin-angiotensin system (RAS) is activated in heart failure, this study tested the hypothesis that attenuation of cardiac SL changes in congestive heart failure (CHF) by angiotensin-converting enzyme (ACE) inhibitors is associated with prevention of alterations in gene expression for SL Na+-K+-ATPase and Na+/Ca2+exchanger. CHF in rats due to MI was induced by occluding the coronary artery, and 3 wk later the animals were treated with an ACE inhibitor, imidapril (1 mg·kg−1·day−1), for 4 wk. Heart dysfunction and cardiac hypertrophy in the infarcted animals were associated with depressed SL Na+-K+-ATPase and Na+/Ca2+exchange activities. Protein content and mRNA levels for Na+/Ca2+exchanger as well as Na+-K+-ATPase α1-, α2- and β1-isoforms were depressed, whereas those for α3-isoform were increased in the failing heart. These changes in SL activities, protein content, and gene expression were attenuated by treating the infarcted animals with imidapril. The beneficial effects of imidapril treatment on heart function and cardiac hypertrophy as well as SL Na+-K+-ATPase and Na+/Ca2+exchange activities in the infarcted animals were simulated by enalapril, an ACE inhibitor, and losartan, an angiotensin receptor antagonist. These results suggest that blockade of RAS in CHF improves SL Na+-K+-ATPase and Na+/Ca2+exchange activities in the failing heart by preventing changes in gene expression for SL proteins.